Conventionally, single screw compressors have been used as compressors for compressing refrigerant or air. For example, Patent Document 1 discloses a single screw compressor including a single screw rotor and two gate rotors.
Such a single screw compressor will be described. The screw rotor is formed in an approximately cylindrical shape, and a plurality of spiral grooves are formed in an outer circumference thereof. The gate rotors are formed in an approximately flat plate-like shape, and are arranged on sides of the screw rotor. A plurality of rectangular plate-like gates are radially provided in the gate rotor. The gate rotor is installed with its rotation axis being perpendicular to a rotation axis of the screw rotor, and the gate is to be engaged with the spiral groove of the screw rotor.
In the single screw compressor, the screw rotor and the gate rotors are accommodated in a casing, and the spiral groove of the screw rotor, the gate of the gate rotor, and an inner wall surface of the casing define a compression chamber. When rotatably driving the screw rotor by an electric motor, etc., the gate rotors rotate in response to the rotation of the screw rotor. Subsequently, the gate of the gate rotor relatively moves from a start point (end portion on a suction side) toward a terminal point (end portion on a discharge side) in the spiral groove with which the gate is engaged, thereby gradually reducing the volume of the completely-closed compression chamber. Consequently, fluid in the compression chamber is compressed.